Electric pressure transducer



Nov. 22, 1955 Filed July 15, 1954 G. M. GlANNlNl ET AL 2,724,760

ELECTRIC PRESSURE TRANSDUCER 2 Sheets-Sheet l Ga e/E1. M GAQIV/VIA/I,flee v M, fines-5x. MA J.

INVENTORS,

Bmzmakg firm/aways,

1955 G. M. GIANNINI ETAL ELECTRIC PRESSURE TRANSDUCER Filed July 15,1954 2 Sheets-Sheet 2 Fire. 53 86 United States Patent ELECTRIC PRESSURETRANSDUCER Gabriel M. Giannini, Pasadena, and Harry M. Riegelman, Jr.,Los Angeles, Calif assignors to G. M. Giannini & Co., Inc., Pasadena,Calif., a corporation of New York Application July 15, 1954, Serial No.443,564

11 Claims. (Cl. 201-48) This invention has to do with pressuretransducers for producing electrical signals in response to variationsof a fluid pressure or difference between fluid pressures.

The invention is concerned more particularly with providing a compactand reliable instrument that is capable of developing one or moreelectrical signals, such, for example, as direct current voltages, thatvary accurately in accordance with the axial extension of a pressureresponsive device.

A primary object of the invention is to provide such an instrument thatis capable of responding to relatively small increments of pressure witha positive and reproducible change of output signal. That isaccomplished by the invention by producing relatively great mechanicalamplification of the initial movement of the pressure responsive elementwithout appreciable friction, backlash or play of any type in themechanical linkages that are employed, and without introducing excessiveresilient restoring force into the overall system. It has beendiscovered that the described characteristics can be providedeffectively by a two-stage amplifying device in which the first stageemploys a lever mounted on fiexure pivots which contribute substantiallyZero friction and play to the system, and a second stage which employs alever mounted on pivot bearings which contribute substantially Zerorestoring force to the system.

A further object of the invention is to produce an instrument of thetype described that is substantially stable against large accelerationsin any direction, whether of sustained or periodic nature.

The invention is further concerned with providing an instrument of thethype described that is lighter and more compact than the most nearlycomparable instruments previously available. At the same time, aninstrument in accordance with the invention is typically capable ofproviding two electrically independent output signals, which mayrepresent diiferent functions of the input pressure difference. As anillustration of the degree of compactness that has been attained withoutsacrifice of the other properties mentioned, the largest overalldimension of an instrument in accordance with the invention may be lessthan twice the diameter of the pressure responsive device and only abouttwice the effective coil length of the potentiometers by Which theoutput signals are developed. For example, in an instrument thatoccupies no more than 15 cubic inches the pressure responsive device maybe a capsule havin a diameter of substantially 2 inches, and the outputsignals may be developed by potentiometer coils having a working surfacenearly 1 /2 inches long and containing 1500 turns or more of wire.

A further aspect of the invention provides particularly convenientadjustment of the degree of amplification, which may be expressed, forexample, as the effective potentiometer coil length per unit lineartravel of the pressure responsive element. Moreover, the output signalmay be made to represent a substantially linear function of the inputpressure difference; or, alternatively,

may be made non-linear, as may be required for various specificapplications. In particular, a preferred type of mechanical linkagebetween the pressure responsive element and the potentiometer brushprovides the advantage of compensating a typical form of nonlinearity ofresponse of such elements, so that even in the presence of suchnon-linearity the overall output may be made to conform very closely,for example within about 1%, to a linear function of the input pressure.

In preferred form of the invention a primary lever is directly driven bythe pressure responsive element, and a plurality of independentlymounted secondary levers are independently linked to that primary lever.Independent output means are connected to the respective secondarylevers. That preferred arrangement has marked advantages of economy,compactness and accuracy of performance. The mounting of the primarylever is-in many respects the most critical aspect of the entireinstrument, since any inaccuracy or play in that mounting is magnifiedby the remainder of the linkage system. Hence the use of a singleprimary lever makes for economy of construction and greatly simplifiesthe entire structure. And the provision of separate secondary levers fordriving each potentiometer permits improved flexibility of operation.For example, relatively fine individual adjustments of those levers canbe provided for compensating detailed differences among potentiometercoils. And radically different functional output responses can beprovided by modifying the proportions and arrangement of one or more ofthe several secondary levers, all without complicating or disturbing themounting of the single primary lever.

A further aspect of the invention concerns a particularly economical andeffective manner of constructing a link for operatively connecting twolevers of a mechanical movement.

A full understanding of the invention and of its further objects andadvantages will be had from the following description of a specificpreferred embodiment, of which description the accompanying drawingsform a part. However, many changes may be made in that embodiment, whichis intended only as illustration and not as a limitation upon the scopeof the invention, that scope being defined in the appended claims.

In the drawings:

Fig. l is a vertical section of an illustrative pressure transducer inaccordance with the invention;

Fig. 2 is a fragmentary section on line 22 of Fig. 1;

Fig. 3 is a plan, showing the instrument with cover removed; and

Fig. 4 is a fragmentary section on line 4-4 of Fig. 2.

As illustratively shown in the drawings, the instrument housingcomprises a base 20, a mounting plate 30 and a cover 34. Base 20comprises a circular plate portion 22, which forms one end wall of theinstrument housing, and a shell portion 24 projecting from the innerface of plate 22. For convenience of description, base plate 22 will beassumed to be horizontal, as shown, with shell portion 24 extendingupward, but it is emphasized that a particular advantage of the presentinstrument is that it may be mounted in any convenient orientation, theposition shown being merely illustrative. Shell portion 24 is externallythreaded at 25 to receive cover 34, which is of cylindrical form withclosed upper end. A suitable pressure seal, indicated at 26, is providedbetween the cover and the base. Mounting plate 30 is rigidly butreleasably mounted on the upper end of shell portion 24, as by thescrews 27, partially enclosing a lower chamber 28 Within the housing.The entire housing defines a main vertical axis 36, about which it hasgeneral cylindrical symmetry.

Pressure responsive means of any suitable type are mounted withinchamber 28. As illustratively shown, such means comprise the capsulewhich is axially extensible in response to variations of the differencein pressure between its interior and exterior. Capsule 40 is coaxiallypositioned in chamber 2% with its lower end rigidly secured to baseplate 22 as by the screw 42 and sealing ring 44. In the embodimentshown, the interior of capsule 49 is evacuated, providing constantinternal pressure; and the pressure to which the instrument isresponsive is admitted to the space surrounding the capsule and withinthe instrument housing, a pressure fitting for the purpose beingindicated at 46. Alternatively, capsule 40 may be so constructed andmounted as to provide a fluid passage between its interior and thecentral threaded well 43 in base 20, which may then receive a secondpressure fitting for supplying a fluid pressure to the interior of thecapsule.

In accordance with one aspect of the invention, the entire mechanism 50for developing one or more electrical signals representing the pressuresupplied to capsule 40 is mounted on the upper face of the removablemounting plate 30. A single connection, shown as the threaded rod 52,extends in spaced relation through a central aperture 54 in plate 39 andoperatively connects capsule 40 to that mechanism. Mechanism 50 can thusbe entirely assembled on mounting plate 3% as a subassembly; and isfully accessible for adjustment merely by removal of cover 34.

As illustratively shown, a single primary lever 69 is supported by twoflexure pivots 64 for limited swinging movement about a horizontalprimary pivot axis 62, spaced from main axis 36. Lever 68 is generallyparallel to plate 30 and spaced above it. Each of the flexure pivotscomprises a fixed block 65 and a movable block 66 connected by crossedleaf springs 67 and 63, both of which pass through the pivot axis.Movable blocks 66 are rigidly mounted directly on the under face oflever 60, as by the screws 69; and fixed blocks 65 are rigidly mountedon the upper face of plate 30 by the screws 71 and the bracket 79.Bracket may be secured to the mounting plate by the screws 72, which areaccessible through clearance apertures 73 in lever 6t and which work inslotted holes in the bracket, permitting convenient adjustment of thespacing between primary pivot axis 62 and main axis 36.

Lever 60 is driven by capsule 49 via a connection, already mentioned,between the upper end of the capsule and the intermediate point of thelever at which it is intersected by main axis 36. That connectiontypically includes the threaded rod 52, rigidly mounted in coaxialposition on the free end of capsule 40, and preferably embodies aflexure pivot 76, which may be of the same type as pivots 64. As shown,the upper block of flexure pivot 76 is rigidly mounted directly on thelower face of lever 30 by the screw 75. The lower block of pivot 76 ismounted on the upper end of threaded rod 52. With that construction, theeffective point of application of the force applied by capsule 4-0 tolever 69 is at the axis 77 of flexure pivot 76. That axis normallyintersects main axis 36 of the instrument, so that the effective leverarm for driving lever 60 is approximately equal to the separation ofprimary pivot axis 62 and main axis 36. The slotted hole 78 by whichflexure pivot 76 is secured to lever 69 permits the pivot to be adjustedlongitudinally of lever 60. When bracket 78 is shifted in the manneralready described, that adjustment permits the axis of flexure pivot 76to be maintained at main axis 36. The effect is then to change theeffective driving lever arm for primary lever 66. Such adjustment of thelever arm is useful, for example, for compensating slight differences ofrate among different capsules 40.

A counterbalancing weight is indicated at 56, mounted as by the screw 57on a relatively short arm of lever 60 that projects outwardly withrespect to main axis 36.

The center of gravity of weight 56 is spaced below the plane of lever60, that spacing being adjustable as by selection of the thickness ofspacer 58. The longitudinal position of the weight on lever 60 is alsoadjustable, as by elongation of the hole in the lever that receivesscrew 57. By means of those adjustments, the effective center of gravityof the entire lever mechanism, including any unbalanced reaction uponlever 60 from the secondary levers to be described, is caused to liesubstantially in primary pivot axis 62. The mechanism may thus be madeto operate substantially independently of impressed accelerations,whether of relatively steady nature, as may be caused by curved flightof an aircraft, or of periodic nature, as may result from vibrationimpressed upon the entire instrument as a unit.

It has been found that to provide adequate stability against impressedaccelerations of the entire instrument flexure pivots 64 should berelatively widely spaced from each other longitudinally of axis 62. Thatspacis at least equal to, and preferably about 50% greater than, theeffective driving lever arm of lever 60, which is the separation of axes62 and 77, as already described.

The use of pivots of flexure type, utilizing crossed springs, both formounting lever 60 and for providing the necessary flexibility of thedriving connection to that lever provides substantially frictionlessoperation and practically eliminates any measurable play or backlash,which if present would be amplified by the remainder of the mechanism,to be described. The resilience of those fiexure pivots introduces anappreciable restoring force into the system, which tends to resistdeflection of lever 60 from its equilibrium position. However, animportant advantage of the present mechanism is the fact that suchrestoring force applied to primary lever 60 has a relatively slighteffect upon the final output of the mechanism, whereas backlash inoperation of that lever would have a relatively amplified effect uponthe output.

The present illustrative embodiment of the invention includes means fordeveloping two electrically independent output signals. Those meanstypically comprise the two potentiometers 80 and 90, including thecircularly curved potentiometer windings 81 and 91 and the contactbrushes 84 and 94, respectively. Windings 81 and 91 are typically formedon relatively flexible cards that are then mounted on the convex facesof arcuate insulating members 83 and 93, supported on brackets 82 and92, respectively. Those brackets are preferably mounted directly on theupper face of mounting plate 30, and are spaced on opposite sides ofprimary lever 60. Windings S1 and 91 may be of various detailedconstruction, providing either linear or tapered resistance as may berequired, and may, for example, be connected alternatively aspotentiometers, as in voltage dividing networks, or as variableresistances, as in bridge networks of various known types.

Brushes 84 and 94 are preferably arranged as shown to engage the curvedinner edges of the respective potentiometer coils. They are resilientlymounted at the free ends of the brush arms 85 and 95. Those arms aremounted for swinging movement about respective secondary pivot axes 86and 96, which preferably coincide with the axes of curvature of windings81 and 91. As shown, those windings, and hence also the potentiometerarms 85 and 95, are coaxial, but the two secondary axes 86 and 96 may bemutually offset. Moreover, the two windings may have different radii ofcurvature and may differ in their electrical characteristics, includingthose already mentioned.

The potentiometer arms 85 and are preferably driven independently fromprimary lever 60, as by the preferred linkage means illustrated. Asshown, the arms 85 and 95 are rigidly, but preferably adjustably,related to respective secondary levers 87 and 97, which are driven fromlever 60 by the respective links 88 and 89. Those links are effectivelyrigid, and are pivotally connected at one end 5 to the respectivesecondary levers and at the other end to the respective arms 89 and 99which are rigidly mounted in axially spaced relation on primary lever60. Those linkages may differ from each other in many particulars ofstructure and adjustment, but are shown substantially identical forclarity of representation. A full description of only one of thoseillustrative linkages will be given.

The link 88 embodies in typical form one aspect of the invention. Theentire link and the flexure piovts by which its ends are connected tolevers 60 and 87 are formed as a unitary structure from a single stripof resilient material such as a beryllium copper alloy, for example.That strip, which may typically be about 0.004 inch thick, islongitudinally folded, for example as shown clearly at 102 in Fig. 4,throughout an intermediate portion of its length. That fold renders thatportion of the thin strip efiectively rigid and capable of transmittinglongitudinal forces in compression as well as in tension. The ends ofthe strip are rigidly connected to the respective levers, relativelyshort portions of the strip being left free between those connectionsand the ends of fold 102. Those unfolded portions, indicated at 103 and104 retain their normal flexibility and permit swinging movement of thelink about its connections to the respective levers. In preferred formof the link, at least part of the unfolded portion at each end of thelink is longitudinally curved in a substantially circular curve ofrelatively short radius of curvature. Each of those curves preferablyextends through an angle at least as great as the total range ofvariation of the angle formed by the link and the lever to which it isconnected. As shown illustratively at 105 and 106, both curves of link88 extend through approximately a right angle in central position of thelinkage. The extreme end portions of the link then lie generallyparallel to the lengths of the respective levers, making their rigidconnection to those levers particularly convenient. Thus, the upper endof link 88 is rigidly connected to arm 89 by the rivets 114, and itslower end is adjustably connected to secondary lever 87 by the screw115.

The described curved portions of the link are preferably supported ontheir concavefaces by correspondingly curved surfaces provided for thatpurpose .on the ends of the respective levers. Such a supporting'curvedsurface on secondary lever 87 is shown illustratively at 110; and onprimary lever arm 89 at 112. It will be seen that as the linkage moves,the resilient strip tends in general to engage a longer portion of oneof those curves and a shorter portion of the other, winding up on onelever and unwinding from the other. Those curved portions of the linkare preferably resiliently pre-stressed, as

by so forming the strip that the angle between its straight endportions, when in relaxed position, lies just outside the range ofvariation of that angle during actual operation of the instrument. Therelatively light resilient restoring force exerted by the link is thenalways in the same direction, tending to minimize play in the secondarypivot bearings to be described.

Arm 89 of primary lever 60, to which the upper end of ling 88 isconnected, might be formed integrally with the lever. However, it ispreferred to provide a bracket-like arm, as shown, which is adjustablymounted on the lever, as by the screws 118 which work in thelongitudinal slot 119. By adjustment of arm 89 longitudinally of lever60, the effective lever arm at which link 88 is driven may beconveniently modified, thereby'changing the amplification of the overalllinkage. Also, by substituting arms 89 of different form, the functionalbehavior of the overall linkage may be modified conveniently.

A particularly convenient and economical structure is shown fortransmitting movement of link 88 to pctentiometer arm 85. Secondarylever 87 is formed integrally with a hub 120, the ends of which arecoaxially recessed to receive journal type jewel bearings 121. Pivotscrews 122 are mounted in aligned threaded holes in the two posts ofbracket 124 and engage bearings 121. P0- tentiometer arm is providedwith clamp means 126, which engages an insulating sleeve placed over hub120, and by which its rotary position with respect to lever 87 isreadily adjustable. With clamp 126 tightened the arm and lever form arigidly related unit. Use of jewel bearings for mounting that unitpermits free rotation through an angle of substantially withoutintroducing any resilient restoring force into the system. The slightplay permitted by such bearings, while it would be objectionable in themounting of primary lever 60, is acceptable in the mounting ofpotentiometer arm 85, since any play of that arm is not furtheramplified before reaching the brush itself.

Normally it might be expected that optimum linearity of the overallsystem would result if the two lever arms connected by link 88 were soarranged as to be parallel when brush 84 is at the mid-point of itsoperating range. However, the described mechanism has been found toprovide a further advantage when that is not the case. Pressureresponsive capsules are sometimes very nearly linear in their movement,but have a general tendency to produce a smaller increment of movementper unit pressure change as they expand. It has been found that thiscommonly encountered type of non-linearity can be compensated remarkablyeifectively by arranging the mechanism so that radii drawn from therespective pivot axes 62 and 86 to the effective ends of link 88, asindicated schematically at 128 and 129, respectively, converge at aslight angle when brush 84 is at mid-position. With that arrangement, ascapsule 40 expands, swinging primary lever 60 upward, the overallamplification of the mechanism tends to increase more rapidly than ifthe described radii were parallel. That increased amplification may bemade to compensate the characteristic decrease in rate of the capsule.

We claim:

1. A pressure transducer, comprising a capsule axially extensible inresponse to pressure variations, a centrally apertured mounting platesupported coaxially of the capsule adjacent one end thereof, structuremounted on the face of the plate opposite to the capsule and definingfirst and second pivot axes parallel to each other and to the plate andspaced on opposite sides of the capsule axis by substantially equaldistances, first and second levers pivotally mounted for swingingmovement about the respective pivot axes, a link connecting the freeends of the levers, said link extending substantially perpendicularly tothe plate at a point spaced outwardly of the second pivot axis, apotentiometer arm carrying a brush at its free end and mounted in fixedrelation to the second lever and movable therewith, an arcuatepotentiometer winding fixedly mounted on the mounting plate in positionto be engaged by the brush, said potentiometer arm and winding beingoifset longitudinally of the said pivot axes with respect to the twolevers, and a driving connection between the capsule and an intermediatepoint of the first lever, said driving connection extending in spacedrelation through the aperture of the mounting plate.

2. In a pressure responsive mechanism of the type that includes anaxially extensible pressure responsive device; first lever meansconnected to the pressure responsive device for amplifying the movementthereof, said first lever means comprising a first lever, first pivotmeans supporting said lever for swinging movement about a first pivotaxis, and a driving connection between the pressure responsive deviceand the lever, and second lever means for amplifying the movement of thefirst lever, said second lever means comprising a second lever, secondpivot means supporting the second lever for swinging movement about asecond pivot axis parallel to the first, a substan tially rigid link,and flexure pivots connecting opposite ends of the link to therespective levers, and signal means responsive to the movement of thesecond lever, said first pivot means comprising two sets of crossedspring hinges spaced longitudinally of the first pivot axis andcontributing substantially zero friction and backlash to the system, andsaid second pivot means comprising a pair of pivot bearings that permitmovement of the second lever through substantially a right angle andcontribute substantially zero restoring force to the system.

3. In a pressure responsive mechanism of the type that includes anaxially extensible pressure responsive device; first lever meansconnected to the pressure responsive device for amplifying the movementthereof, said first lever means comprising a first lever, first pivotmeans supporting said lever for swinging movement about a first pivotaxis, and a driving connection between the pres sure responsive deviceand the lever, and second lever means for amplifying the movement of thefirst lever, said second lever means comprising a second lever, secondpivot means supporting the second lever for swinging movement about asecond pivot axis parallel to the first, a substantially rigid link, andflexure pivots connecting opposite ends of the link to the respectivelevers, and signal means responsive to the movement of the second lever,said link and fiexure pivots comprising a unitary structure consistingof a single strip of thin resilient material having a longitudinal foldthroughout an intermediate portion of its length, opposite end portionsof the strip being connected rigidly to the respective levers, and saidend portions of the strip being spaced longitudinally from therespective ends of the said intermediate portion.

4. In a pressure responsive mechanism of the type that includes anaxially extensible pressure responsive device; first lever meansconnected to the pressure responsive device for amplifying the movementthereof, said first lever means comprising a first lever, first pivotmeans supporting said lever for swinging movement about a first pivotaxis, and a driving connection between the pressure responsive deviceand the lever, and second lever means for amplifying the movement of thefirst lever, said second lever means comprising a second lever, secondpivot means supporting the second lever for swinging movement about asecond pivot axis parallel to the first, a substantially rigid link, andflexure pivots connecting opposite ends of the link to the respectivelevers, and signal means responsive to the movement of the second lever,said link and fiexure pivots comprising a unitary structure consistingof a single strip of thin resilient material having a longitudinal foldthroughout an intermediate portion of its length, portions of the stripadjacent both ends of said fold being substantially circularly curved,end portions of the strip outwardly of said curved portion being rigidlyconnected to the respective levers, and the respective curved portionsof the strip extending through angles that are greater than therespective ranges of variation of the angles formed by the intermediateportion of the strip and the respective levers.

5. In a pressure responsive mechanism of the type that includes anaxially extensible pressure responsive device; first lever meansconnected to the pressure responsive device for amplifying the movementthereof, said first lever means comprising a first lever, first pivotmeans supporting said lever for swinging movement about a first pivotaxis, and a driving connection between the pressure responsive deviceand the lever, and second lever means for amplifying the movement of thefirst lever, said second lever means comprising a second lever, secondpivot means supporting the second lever for swinging movement about asecond pivot axis parallel to the first, a substantially rigid link, andflexure pivots connecting opposite ends of the link to the respectivelevers, and signal means responsive to the movement of the second lever,said link and fiexure pivots comprising a unitary structure consistingof a single strip of thin resilient material having a longitudinal foldthroughout an intermediate portion of its length, portions of the stripadjacent both ends of said fold being curved through respective anglesthat are greater than the ranges of variation of the angles formed bythe intermediate portion of the strip and the respective levers, endportions of the strip outwardly of said curved portions being rigidlyconnected to the respective levers, and the levers having curvedsurfaces that correspond in curvature to the respective curved portionsof the strip and that normally support the concave faces of said curvedportions.

6. In a mechanical movement, two levers pivoted on respective mutuallyspaced parallel pivot axes, and a driving connection between the leverscomprising a single strip of thin resilient material having alongitudinal fold throughout an intermediate portion of its length, andmeans rigidly connecting opposite end portions of the strip to therespective levers, said end portions being spaced longitudinally fromthe respective ends of the said intermediate portion.

7. In a mechanical movement, two levers pivoted on respective mutuallyspaced parallel pivot axes, and a driving connection between the leverscomprising a single strip of thin resilient material having alongitudinal fold throughout an intermediate portion of its length, endportions of the strip spaced from said intermediate portion beingrigidly connected to the respective levers, the strip beinglongitudinally curved between the intermediate portion and the said endportions.

8. In a pressure responsive mechanism of the type that includes anaxially extensible pressure responsive device and a plurality ofelectrically independent output means responsive to said device; primarylever means connected to the pressure responsive device for amplifyingthe movement thereof, said primary lever means comprising a primarylever, primary pivot means supporting said lever for swinging movementabout a primary pivot axis normal to the axis of the pressure responsivedevice, and a driving connection between the pressure responsive deviceand the lever, a plurality of secondary lever means for amplifying themovement of the primary lever, said secondary lever means comprisingrespective secondary levers, pivot means supporting the secondary leversindependently for swinging movement about respective secondary pivotaxes, and respective driving connections between the several secondarylevers and the primary lever, and independent driving connectionsbetween the several secondary levers and the respective output means.

9. In a pressure responsive mechanism of the type that includes anaxially extensible pressure responsive device and a plurality ofelectrically independent output means responsive to said device; primarylever means connected to the pressure responsive device for amplifyingthe movement thereof, said primary lever means comprising a primarylever, primary pivot means supporting said lever for swinging movementabout a primary pivot axis normal to the axis of the pressure responsivedevice, and a driving connection between the pressure responsive deviceand the lever, a plurality of secondary lever means for amplifying themovement of the primary lever, said secondary lever means comprisingrespective secondary levers, pivot means supporting the secondary leversindependently for swinging movement about respective secondary pivotaxes, and respective driving connections between the several secondarylevers and the primary lever, each of the last said driving connectionsincluding independently adjustable means for varying the relationshipbetween the movement of the associated secondary lever and the movementof the primary lever, and independent driving connections between theseveral secondary levers and the respective output means.

10. In a pressure responsive mechanism of the type that includes anaxially extensible pressure responsive device and a plurality ofelectrically independent output means responsive to said device; primarylever means connected to the pressure responsive device for amplifyingthe movement thereof, said primary lever means comprising a primarylever, primary pivot means supporting said lever for swinging movementabout a primary pivot axis normal to the axis of the pressure responsivedevice, and a driving connection between the pressure responsive deviceand the lever, a plurality of secondary lever means for amplifying themovement of the primary lever, said secondary lever means comprisingrespective secondary levers, pivot means supporting the secondary leversindependently for swinging movement about respective secondary pivotaxes, substantially rigid links pivotally connecting the free ends ofthe respective secondary levers and the primary lever, means on theprimary lever for independently varying the radial distances from theprimary pivot axis to the points of connection of the respective links,and independent driving connections between the several secondary leversand the respective output means.

11. In a pressure responsive mechanism of the type that includes acapsule axially extensible in response to pressure variations, the rateof the capsule decreasing with increasing extension thereof, primarylever means connected to the capsule for amplifying the movementthereof, said primary lever means comprising a primary lever, primarypivot means supporting said lever for swinging movement about a primarypivot axis normal to the capsule axis, and a driving connection betweenthe capsule and the lever, secondary lever means for amplifying themovement of the primary lever, said secondary lever means comprising asecondary lever, pivot means supporting the secondary lever for swingingmovement about a secondary pivot axis parallel to the first, asubstantially rigid link, means pivotally connecting the opposite endsof the link to the respective levers, and output means responsive tomovement of the secondary lever within a predetermined range of movementthereof, the radii drawn from the primary and secondary pivot axes tothe respective ends of the link converging at an oblique angle when thesecondary lever is at the mid-point of its said range of movement.

No references cited.

